Four Zen monks were meditating in a monastery. All of a sudden the prayer flag on the roof started flapping.
The younger monk came out of his meditation and said: "Flag is flapping"
A more experienced monk said: "Wind is flapping"
A third monk who had been there for more than 20 years said: "Mind is flapping."
The fourth monk who was the eldest said, visibly annoyed: "Mouths are flapping!"